The present invention relates to a breather apparatus of a crankcase, in which a crankshaft is rotatably supported and lubricating oil is accommodated in a bottom of a crank chamber thereof.
In the crank chamber of an engine, the lubricating oil supplied to mutual sliding portions of parts assembled in the crank chamber is accommodated. This lubricating oil is agitated by an oil scraper or oil pickup generally attached to the crankshaft and becomes oil mist with which the inside of the crank chamber is filled. Meanwhile, to eliminate pressure fluctuation occurring in the crank chamber owing to operations of the engine, a breather hole for ventilating the inside and outside of the crank chamber is provided in the crankcase. Therefore, to reduce consumption of the lubricating oil, it is necessary to prevent the lubricating oil from leaking out from the breather hole.
Thus far, there has been known a technology for preventing oil components from leaking out, by providing the breather hole in an exit of the complicated breather chamber and preventing oil components larger in specific gravity than gas components from reaching the breather hole. For example, in the technology disclosed in Patent Document 1 (Japanese Patent Laid-open No. 2001-329827), a breather chamber is formed at a top of a crankcase and a gap is provided between the breather chamber and a timing chain chamber, so that an oil-component mixed gas in the crankcase is made to flow through this gap into the breather chamber. Further, to improve a gas-liquid separating action, a bulkhead is provided so as to protrude therefrom on the way of the gap. In the same manner, in the technologies disclosed in, for example, Patent Document 2 (Japanese Patent Laid-open No. 2002-256838) and Patent Document 3 (Japanese Patent Laid-open No. 2001-65326), a breather chamber having a predetermined volume is provided to return oil components contained in an oil-component mixed gas, to the crank chamber.